Lamp

ABSTRACT

A lamp includes a glass bulb  2  with a concave portion  1 , a base  7  attached so as to cover at least part of the concave portion, a lead  11  for supplying electrical power with an end section located in the concave portion  1 , and lead-free solder  17 . The lead free solder  17  is composed mainly of Sn, and further contains, at least, between 5% and 40% inclusive of Sb and between 0% and 10% inclusive of Cu by mass, and has a solidus temperature of at least 235° C.

TECHNICAL FIELD

The present invention relates to halogen lamps, HID lamps and the like.

BACKGROUND ART

Lamps such as metal halide lamps commonly include a glass bulb (externalbulb) with a concave portion formed at one end part, and an E-type basethat is fixed to the one end of the glass bulb and has an eyelet partand a shell part.

A arc tube with electrodes disposed therein is provided inside the glassbulb.

Further, two leads for supplying electrical power to the electrodesextend out from the end of the glass bulb that is at the base.

One of the leads extends through a through hole provided in the eyeletpart of the base, and is soldered to the outside surface of the eyeletpart to form an electrical connection with the eyelet part.

The other lead extends from the concave section of the glass bulb, andpasses between the glass bulb and the shell part of the base, beingelectrically connected to the shell part by solder poured into a gapbetween the concave portion and the base.

The solder poured into the gap between the concave portion and the baseconnects to the glass bulb and the base, and further functions toprevent the base from rotating with respect to the glass bulb.

Note here that, during metal halide lamp operation, the temperature ofthe base reaches 200° C. or more due to the heat generated in the arctube. Hence, the solder used in the base section must not only be a hightemperature solder, but one that does not melt even at temperatures of200° C. or more.

Note that, in this specification, a solder whose solidus temperature is183° C., the melting point of Pb-63Sn, or more is referred to as a hightemperature solder.

Conventionally, solders such as Pb-20Sn and Pb-10Sn, which are describedin JIS Z 3281 (1999), have been widely used as high temperature soldersin the base section of lamps. Such high temperature solders, whose mainconstituent is Pb, have good solderability with respect to bases madefrom brass, nickel plated brass and the like.

Note that the “good solderability”referred to here means, in terms ofthe manufacturing process, that solder wire can be used, that solder iseasily fed into the soldered section, and that the melted solder setsquickly; and in terms of solder quality, that respective alloy layersare formed between the lead material, the solder and the base material,and that the formed electrical connections are stable.

However, in recent years, due to environmental considerations,regulation against the use of high temperature solder with lead as themain constituent has continued globally. For this reason, there is astrong demand for lead-free solder, which does not include Pb.

To realize such a lead-free solder, solders containing Sn as their mainconstituent, and including other appropriately added elements have beenexamined.

Specifically, an alloy composed of mainly of Sn, containing between 1%and 2.5% exclusive of Cu by mass, has been proposed as a lead-freesolder for use in lamps (see laid open Japanese patent application2002-245974).

However, when lamps using this type of lead-free solder composed of anSn—Cu alloy were used, for instance, in low temperature conditions wherethe temperature of the surroundings reached −40° C., a problem occurred.This problem was cracking in the soldered section, causing poorconduction between the leads and the base.

On consideration of this problem, the following conclusions could bedrawn.

Namely, if a lamp is used in low temperature conditions where theambient temperature is −40° C., when the lamp is not operating, thetemperature of the base is the same as the temperature of thesurroundings, which is −40° C. However, when operating, the temperatureof the base is 200° C. or more. Hence, the temperature differencebetween the on and off states for the lamp is extremely large.

Moreover, if the lead free solder composed of Sn and Cu approaches orexceeds its solidus temperature, as is it does when the lamp is on, evensupposing it does not melt, its bonding strength will be much reduced.

Due to the factors described above, it may be concluded that that, whena lamp is switched from on to off, the base temperature falls quicklyfrom a high temperature of 200° C. or more to a very low temperature,the solder comes under a large stress because of the differing rates ofthermal expansion for the solder and the base, and cracking occurs inthe in the soldered section.

Further, in lamps using lead-free solder composed of Sn and Cu theproblem occurred whereby the leads easily separated from the solder.

This problem is considered to occur because of insufficientheat-resistance in the lead-free solder.

DISCLOSURE OF THE INVENTION

The present invention was conceived in order to solve the statedproblems, and has a particular object of providing a lamp usinglead-free solder in which cracking does not occur in the solderedsection, when the lamp is used in an environment where the temperaturedifference between the on and off states of the lamp is very large. Afurther object is to provide a lamp in which the separation of the leadsand the lead free solder used in the lamp is prevented by increasing theheat resistance of the lead-free solder.

In order to achieve the objects described above, the present inventionis lamp including: a glass bulb; a base attached to one end of the glassbulb; leads for supplying electrical power; and lead-free solderelectrically connecting the leads to the base, wherein the lead-freesolder is composed mainly of Sn, further contains, at least, between 5%and 40% inclusive of Sb and between 0% and 10% inclusive of Cu by mass,and has a solidus temperature of at least 235° C.

With this construction, separation of the leads from the solder can beprevented because the heat resistance of the solder is higher than thatof conventional lead-free solder. Further, cracking does not occur inthe soldered section, even when the lamp is used over a long period incold conditions, where the temperature difference between the on and offstates of the lamp is very large.

Consequently a longer lamp lifetime can be achieved.

Further, the present invention is a lamp including: a glass bulb havinga concave portion; a base attached to the glass bulb so as to cover atleast part of the concave portion; a lead for supplying electrical powerhaving an end section located in the concave portion; and lead-freesolder poured into the concave section to electrically connect the baseand the lead, wherein the lead-free solder is composed mainly of Sn,further contains, at least, between 5% and 40% inclusive of Sb andbetween 0% and 10% inclusive of Cu by mass, and has a solidustemperature of at least 235° C.

With this construction, separation of the lead from the solder can beprevented because of the improvement in the heat resistance of thesolder. Further, cracking does not occur in the solder, even when thelamp is used over a long period in very cold conditions where thetemperature difference between the on and off states of the lamp is verylarge.

Also, since the tensile strength (Pa) of the lead-free solder is high,even when a torque is applied between the base and the glass bulb, thelead-free solder resists deformation. Thus, the base can be reliablyprevented from rotating with respect to the glass bulb.

Further, the lead-free solder may further contain Ni, Co, Fe, Mo, Cr,and Mn with a combined mass content of between 0% and 0.5% inclusive.With this construction, the flow characteristics of the lead-free solderare better, and the solderability of the lead-free solder can thereforebe improved.

Further, the lead free solder may further contain Ag and Bi with acombined mass content of between 0% and 1% inclusive. With thisconstruction, the heat resistance of the solder can be further improved.

Further, the lead-free solder may further contain at least one of P, Geand Ga, and a combined mass content of P, Ge, and Ga be between 0.001%and 0.05% inclusive. With this construction, the oxidation resistance ofthe solder can be improved, and the increase in contact resistance dueto oxidation at the surface of the solder can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view with cut-away section of a metal halide lamp thatis an embodiment of the present invention;

FIG. 2 is an enlarged elevation of part of the metal halide lamp;

FIG. 3 is an enlarged cross-sectional view of a part of glass bulb usedin the metal halide lamp; and

FIG. 4 is a table showing the melting temperature and temperature cycletest results for lead-free solders of varying composition.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described below with referenceto the drawings.

As shown in FIG. 1, the metal halide lamp of the embodiment of thepresent invention includes a glass bulb 2 with an internal arc tube 6,and a base 7 attached so as to cover at least part of a concave portion1 (see FIG. 2) of the glass bulb 2.

The glass bulb 2 may, for example, be made from hard glass or quartzglass.

A stem section 3 is provided inside the glass bulb 2 at the base end ofthe glass tube, and two stems 4 a and 4 b are sealed into to the stemsection 3. The two stems 4 a and 4 b sealed into the stem section 3 haveend parts that extend from the stem section 3 into the glass bulb 2.

The end parts of the stems 4 a and 4 b on the stem section 3 sideconnect to leads 10 and 11, and the end parts that extend inside theglass bulb 2 connect to power supply lines 5 a and 5 b.

As well as supplying electrical power to electrodes 9 a and 9 b insidethe arc tube 6, the pair of power supply lines 5 a and 5 b reinforce thearc tube 6.

The arc tube 6 includes an emission section 18 that forms a dischargespace within which the pair of electrodes 9 a and 9 b are disposed so asbe opposite one another. Sealing parts 19 a and 19 b are provided atrespective ends of the emission section 18.

Metal iodides, mercury, inert gases and the like are each enclosed inthe emission section 18 in predetermined quantities.

The two electrodes 9 a and 9 b are connected to exterior leads 21 a and21 b via molybdenum foil 20 a and 20 b, which is sealed inside thesealing parts 19 a and 19 b. The exterior leads 21 a and 21 b connect tothe power supply lines 5 a and 5 b.

The base 7 is a screw type (E-type) base.

As shown in FIG. 2, the concave portion 1 and thread section 8 areprovided on the end of the glass bulb to which the base 7 is attached.

As shown in FIG. 3, the base 7 includes the eyelet part 13 with acentral through hole 12, and a shell part 15 that is provided via aglass insulator 14 in the eyelet part 13. The eyelet part 13 and theshell part 15 may be made of a material such as nickel-plated brass.Note here that FIG. 2 shows FIG. 3 as seen along direction X.

The shell part 15 of the base 7 and the thread section 8 of the glassbulb 2 are screwed together, and thereby mechanically attached.

One of the leads 10 is passed through a through hole 12 that is providedthrough the bottom surface of the base 7, and is soldered to theexterior surface of the eyelet part 13 using lead-free solder 16.

Extending out of the other side of the glass bulb 2, the other lead 11passes between the glass bulb 2 and the shell part 15 where the concaveportion 1 is located.

Further, the other lead 11 is electrically connected to the shell part15 via lead-free solder 17, which is poured into the gap between theconcave portion 1 and the base 7.

Here, at the concave portion 1, the lead-free solder 17 is in contactwith both the glass bulb 2 and the base 7, and functions to preventrotation, particularly reverse rotation, of the base 7 with respect tothe glass bulb 2.

Note that suitable decisions about details such as the shape and depthof the concave portion 1 are made after considering hereafter describedfactors such as the quantity of solder to be poured into the gap and thetype of pouring method.

The lead-free solder 16 and 17 is composed mainly of Sn, furthercontains, at least, between 5% and 40% inclusive of Sb and between 0%and 10% inclusive of Cu by mass, and has a solidus temperature of atleast 235° C.

Note that, though the term “lead-free” may be intended for a solder withno added lead whatsoever, in this specification the term “lead-free”also covers the case where small quantities of lead have unavoidablybecome mixed into the solder.

If the Sb content of a solder is less than 5% by mass, the solidustemperature drops below 235° C., and the heat resistance drops. Becauseof the drop in the heat resistance, such solders are found to beinappropriate for use in the base 7 whose temperature reaches 200° C. ormore when the lamp is on. If, on the other hand, the Sb content exceeds40% by mass, the solder becomes brittle, and is found to detach easilyafter an externally applied impact to the soldered section. Hence, theSb mass content has been set between 5% and 40% inclusive.

Further, if the Cu content exceeds 10% by mass, the liquidus temperaturereaches at least 450° C., and a soldering temperature of at least 450°C. is necessary. If the soldering temperature exceeds 450° C., however,fracture may occur due to distortions in the glass section of the lampcaused by the heat, and the soldering process may become more difficult.

Here, for the remaining constituents of the lead-free solder 16 and 17,it is preferable that the total content of Ni, Co, Fe, Mo, Cr and Mntogether is 0.5% or less by mass, so as to improve the solder flowcharacteristics and improve the strength of the joints between the base7 and the leads 10 and 11.

Further, for the remaining constituents of the lead-free solder 16 and17, it is preferable that the total content of Ag and Bi together is 1%or less by mass, so as to improve the heat resistance.

Moreover, for the remaining constituents of the lead-free solder 16 and17, it is preferable that the solder contains at least one of P, Ge, andGa, and that the total content of these constituents together is between0.001% and 0.05% inclusive by mass.

This is because it was found that, if the total content of theseconstituents is less than 0.001% by mass, acid resistance of the soldercannot be sufficiently improved, and on the other hand, if the totalcontent exceeds 0.05% by mass, solderability may be reduced.

Experiments were performed to ascertain the operating performance ofmetal halide lamps of the embodiment of the present invention.

First, the metal halide lamps of the embodiment of the present inventionwere produced using the lead-free solder 16 and 17 of the variouscompositions shown in FIG. 4.

Then, in each of the various lamps, the melting temperature of thelead-free solder 16 and 17 was measured, a temperature cycle testperformed, and the results shown in FIG. 4 obtained.

Note that the metal halide lamps of the examples for comparison 1 to 5only differ from the metal halide lamps of the embodiment of the presentinvention in terms of the composition of the solder, and are otherwiseidentical in construction.

The melting temperature measurements and the temperature cycle tests ofFIG. 4 were performed in the following manner.

Melting temperature measurement: solidus and liquidus temperatures weremeasured using differential thermal analysis following the standards setout in JIS Z 3198 (2003).

Temperature cycle test: the lamps were subjected to a heat cycle duringwhich each lamp was first left for 30 minutes in an environment wherethe ambient temperature was −40° C. and then left for 30 minutes in anenvironment where the ambient temperature was 200° C. The number ofcycles before for cracking occurred in the soldered section of base 7was then counted. If cracking had not occurred by the 250^(th) cycle thelamp was considered to be durable enough for long term use (for theduration of the rated lifetime, for instance), and the lamp was judgedto be “satisfactory”. On the other hand, lamps in which crackingoccurred before the 250 cycles were completed were judged to have“failed”.

As is clear from FIG. 4, it was discovered that, by setting thecomposition of the lead-free solder 16 and 17 to contain Sn as the mainconstituent, and further contain, at least, between 5% and 40% inclusiveof Sb and 10% or less of Cu by mass, a solidus temperature of at least235° C. could be achieved, and hence, the heat resistance of the soldercould be improved, separation of the lead-free solder 16 and 17 from theleads 10 and 11 could be prevented, and cracking in the soldered sectioncould be prevented over long periods of use. As a result, poorconduction between the leads 10 and 11 and the base 7 could beprevented, and a longer lifetime for the lamp could be achieved.

On the other hand, in the case of the examples for comparison 1 to 5, itwas discovered that the solidus temperature was less than 235° C., theheat resistance was insufficient, and cracking occurred in the solderedsection.

Next, for each of the examples of the invention 1 to 26 and the examplesfor comparison 1 to 5, a torque of 10 Nm, the level generated when alamp is removed from its socket (not shown), was applied to the base 7to ascertain whether or not the base 7 would rotate with respect to theglass bulb 2.

Note that, in the Japanese Industrial Standard (JIS C7604), the standardbase torque endurance in terms of twisting moment for a E26 type base is2 Nm. However, here, the reference value set to 10 Nm with practical usein mind.

From the result of this test, it was discovered that base 7 did notrotate with respect to the glass bulb 2 in the examples of the invention1 to 26. This is considered to be because the tensile strength of thelead-free solder 17 in examples 1 to 26 was high, and because thelead-free solder 17 did not deform even when a force acted in therotation direction on the base 7 with respect to the glass bulb 2.

On the other hand, in the examples for comparison 1 to 5, the base 7 didrotate, if only by a small amount, with respect to the glass bulb 2.This maybe considered to be because the tensile strength of the solderin the examples for comparison was low, and hence, part of the lead freesolder did deform when a force acted in the rotation direction on thebase 7 with respect to the glass bulb 2.

Hence, by using a lead-free solder 17 composed mainly of Sn, furthercontaining, at least, between 5% and 40% inclusive of Sb and 10% or lessof Cu by mass, with a solidus temperature of at least 235° C. to connectthe lead 11 and the shell part 15, rotation of the base 7 with respectto the glass bulb 2, in particular, can be reliably prevented.

Note that, as examples of the tensile strength of the solder, inexamples of the present invention 1, 2, 13, and examples for comparison1, 2 and 5, the tensile strength of the of the solder was 30 MPa, 58MPa, 90 MPa, 28 MPa, 32 MPa and 41 MPa respectively.

Note also that though in the above embodiment the case where the solderused between the lead 10 and the eyelet part 13, and the solder usedbetween the lead 11 and the shell part 15 are both the same lead-freesolder 16 and 17 has been described, the composition of lead-free solder16 and 17 may be varied.

Further, though described in the above embodiment with a regular halidelamp as an example, the present invention is not limited to such a lamp,and can also be suitably applied, for example, in high pressure sodiumand xenon type high pressure discharge lamps, halogen electric lightbulbs, incandescent bulbs and the like.

INDUSTRIAL APPLICABILITY

The lamp of the present invention can be used in lamp applications andthe like, where it is necessary that separation of the leads from thesolder can be prevented, and further, where it is necessary that a poorconnection between the base and the leads resulting from coldenvironment use when there is a large temperature difference between theon and off states can be prevented.

1. A lamp comprising: a glass bulb; a base attached to one end of theglass bulb; leads for supplying electrical power; and lead-free solderelectrically connecting the leads to the base, wherein the lead-freesolder is composed mainly of Sn, further contains, at least, between 5%and 40% inclusive of Sb and between 0% and 10% inclusive of Cu by mass,and has a solidus temperature of at least 235° C.
 2. A lamp comprising:a glass bulb having a concave portion; a base attached to the glass bulbso as to cover at least part of the concave portion; a lead forsupplying electrical power having an end section located in the concaveportion; and lead-free solder poured into the concave section toelectrically connect the base and the lead, wherein the lead-free solderis composed mainly of Sn, further contains, at least, between 5% and 40%inclusive of Sb and between 0% and 10% inclusive of Cu by mass, and hasa solidus temperature of at least 235° C.
 3. The lamp of claim 1,wherein the lead-free solder further contains Ni, Co, Fe, Mo, Cr, and Mnwith a combined mass content of between 0% and 0.5% inclusive.
 4. Thelamp of claim 1, wherein the lead free solder further contains Ag and Biwith a combined mass content of between 0% and 1% inclusive.
 5. The lampof claim 1, wherein, the lead-free solder further contains at least oneof P, Ge and Ga, and a combined mass content of P, Ge, and Ga is between0.001% and 0.05% inclusive.
 6. The lamp of claim 2, wherein thelead-free solder further contains Ni, Co, Fe, Mo, Cr, and Mn with acombined mass content of between 0% and 0.5% inclusive.
 7. The lamp ofclaim 2, wherein the lead free solder further contains Ag and Bi with acombined mass content of between 0% and 1% inclusive.
 8. The lamp ofclaim 2, wherein, the lead-free solder further contains at least one ofP, Ge and Ga, and a combined mass content of P, Ge, and Ga is between0.001% and 0.05% inclusive.